Axial Compression Performance Of Reinforced Concrete Columns Reinforced With Fiber Grid ECC After Fir

Fires bring great harm to socio-economic and natural resources.Building fires account for a large proportion of all fires,and due to the influence of fire,the strength of steel and concrete is attenuated,and the bearing capacity of column sections is reduced.Post-fire safety assessment of partially damaged reinforced concrete columns and post-fire repair became a key issue.In recent years,fiber grid reinforced ECC materials have been widely used in the field of structural reinforcement,which not only gives full play to the advantages of excellent alkali resistance,high tensile strength and deformation resistance of fiber grids,but also gives full play to the characteristics of high tensile strain and ultra-high toughness of ECC materials,which can effectively improve the axial compressive performance of reinforced concrete columns.In view of the research on the reinforcement of reinforced concrete columns after fire,the axial compression test and numerical simulation of reinforced concrete columns reinforced after fire reinforced by nine fiber grilles reinforced ECC are carried out,and finally the bearing capacity calculation formula of reinforced columns after fire is obtained by theoretical analysis.The specific research is as follows:(1)In order to better simulate the stress state of reinforced concrete columns in actual engineering,axial force is applied to the specimen before heating,an open flame heating test is carried out according to the ISO 834 curve,and different methods are used to strengthen after natural cooling,and axial pressure test is carried out after 28 days of curing.The test mainly considers the thickness of the reinforcement layer,the number of fiber grid layers,the fire time and whether the reinforcement layer is directly compressed,and the influence of the above factors on the peak bearing capacity and axial deformation capacity of the reinforcement column is studied.The test shows that the fiber grille reinforced ECC reinforcement layer has a good restraining effect on the reinforced concrete column after fire,changes the failure form of the reinforced concrete column,and increases the axial deformation ability of the concrete column.Compared with the unreinforced column,the peak bearing capacity of the reinforced column is increased by 42.0%-60.84%.When the thickness of the reinforcement layer increases from 10 mm to 20 mm,the axial deformation ability of the specimen increases,and the displacement ductility coefficient increases.When the number of fiber grid layers increases from 0 to 2 layers,the bearing capacity of the specimen first increases and then decreases.The test shows that the 20 mm thickness ECC and 1 layer fiber grille have the best reinforcement effect.(2)The finite element model of the main body was established by ABAQUS software,and the influence of various parameters on the peak bearing capacity and axial deformation of the reinforced column in the test was simulated,and the temperature field distribution of the reinforced concrete column,the load-displacement curve of the reinforced column,the strain curve of the fiber grid and the strain curve of the steel bar were obtained,and the peak load of the specimen was in good agreement with the test value,and the error was less than 15%.For concrete and ECC,the cracking and failure of the components were judged by the principal stress(S)and equivalent plastic strain(PEEQ)clouds,and the yield of the steel bars and the tensile of the fiber grid were judged by the Mises cloud.The finite element software was used to analyze the fire time,stirrup ratio and core concrete strength parameters,and it was found that when the fire time increased from 30 min to 120 min,the peak load,axial compressive stiffness and displacement ductility coefficient of the specimen decreased.With the increase of reinforcement ratio,the peak load,axial compressive stiffness and displacement ductility coefficient of the specimen increase.As the strength of the concrete in the core area increases,the peak load,axial compressive stiffness and displacement ductility coefficient of the specimen increase.(3)The peak bearing capacity of reinforced concrete columns after fire reinforced with fiber grille reinforced ECC is theoretically derived.Based on the experimental data,the existing theoretical model of reinforcement layer is modified,and according to the superposition theory,the bearing capacity calculation formula of reinforced concrete columns reinforced after fire reinforced ECC reinforced by fiber grid is proposed,and the theoretical analysis calculation value is compared with the experimental value,and the results show that the consistency between the two is high,and the theoretical calculation formula can better predict the bearing capacity of reinforced concrete columns after fiber grid reinforced ECC reinforcement after fire..